The present invention relates generally to semiconductor wafer processing, and more particularly to wafer carriers for retaining semiconductor wafers during processing operations.
In conventional wafer processes, such as a polishing operation, a wafer carrier C (shown in section in FIG. 7) is used to retain a plurality of wafers W (one is shown) during the operation. The wafer carrier is typically a thin, flat plate, usually made of metal, disposed between the polishing pads P of the polishing machine. The plate has several large circular holes cut therein, each hole being sized larger than a wafer to be received therein. Conventional carriers may include a molded ring R permanently affixed to the plate and extending inwardly from the edge of each hole. The ring acts as a buffer between the wafer and the metal plate in order to protect the edge of the wafer from chipping or other damage. The ring and the plate must be of appropriate thickness, i.e., slightly thinner than the wafer, so that the pads of the polishing machine will contact substantially the entirety of both sides of the wafer. The ring is made of plastic or another material which is softer than the metal plate to protect the wafer edges from engaging the metal plate during operation, which can damage the wafer.
The carrier and insert are both worn down by the polishing operation. As shown graphically in FIG. 8, the plastic ring will wear down (i.e., become thinner) more rapidly than the metal plate during repeated cycles in the lapping or polishing machine. For example, after about 80 hours of polishing operation, the metal thickness is reduced about 4 microns, while the ring thickness is reduced about 16 microns. It is known that thinning of the ring negatively affects the quality of the processed wafer. The thin ring, as shown in FIG. 7, causes the pads to deform outward away from the wafer edge. Such deformation of the pads causes the wafer to be thicker at a peripheral edge margin (sometimes referred to as a xe2x80x9cdog-bonexe2x80x9d shape), as shown in FIG. 7A. (The thickness of the wafer edge margin and the difference in thickness between the wafer and the ring is exaggerated for illustration purposes.) Conventional carriers having rings which are too thin cannot be repaired, but rather must be replaced entirely. Since carriers are expensive, they tend to be replaced too infrequently, thereby negatively affecting the quality of the wafers produced toward the end of the useful life of the carrier.
It is further known that the softness of the plastic material conventionally used for the ring may negatively affect the shape of the wafer edge E. The soft material causes more friction to be created between the wafer and the ring which causes increased wear of the wafer material at the wafer edge E. Moreover, the friction increases the temperature at the wafer edge which increases the rate of chemical reaction between the polishing slurry and the wafer material at the wafer edge. The rate at which the slurry removes wafer material from the wafer edge is thereby increased. Thus, as shown in FIG. 7A, the edge of the wafer polished using the conventional carrier having the conventional ring typically has a flattened edge due, at least in part, to the increased friction between the wafer and the ring.
Among the several objects of the present invention may be noted the provision of a method of repairing a wafer carrier that extends the useful life of the wafer carrier; the provision of such a method that improves the flatness of processed semiconductor wafers; the provision of such a method that improves the edge shape of processed semiconductor wafers; and the provision of such a method which is economical and easy to perform.
Further among the several objects of the present invention may be noted the provision of a wafer carrier for retaining a plurality of semiconductor wafers in a processing apparatus which is easily repairable; the provision of such a wafer carrier which has a longer useful life; and the provision of such a wafer carrier which is economical for use in processing wafers.
Briefly, a method of the present invention is directed to repairing a wafer carrier after plural processing operations during which the carrier holds a plurality of semiconductor wafers in a processing apparatus which removes wafer material by at least one of abrading and chemical reaction. The wafer carrier has holes therein for receiving respective ones of the wafers and removable annular inserts for each hole. Each insert is receivable in a respective one of the holes for engaging a peripheral edge of one of the wafers. The thickness of the insert is reduced during the successive processing operations. The method comprises removing at least one of the inserts from the wafer carrier and installing at least one new insert in the wafer carrier having a thickness substantially greater than a minimum thickness to extend the useful life of the wafer carrier and to improve the flatness and parallelism of surfaces of wafers processed using the wafer carrier.
Another aspect of the invention is a wafer carrier for retaining a plurality of semiconductor wafers in a processing apparatus during a processing operation which removes wafer material by at least one of abrading and chemical reaction. The processing apparatus is adapted for removing wafer material from a front surface and a back surface of each wafer simultaneously. The wafer carrier comprises a blank of material having an opening therein. An insert is disposed in the opening for receiving one of the wafers and engages a peripheral edge of the wafer to hold the wafer as the carrier rotates so as to inhibit damage to the edge of the wafer during the processing operation. The insert is removably engageable with the carrier in the opening. The insert is releasably held in the opening such that the insert can be non-destructively removed and replaced with another insert for extending the useful life of the wafer carrier and to improve the flatness and parallelism of the front and back surfaces of the wafers processed using the wafer carrier.
Yet another aspect of the invention is a method of processing a plurality of semiconductor wafers in a processing apparatus which removes wafer material by at least one of abrading and chemical reaction comprising placing a wafer carrier in the apparatus. The wafer carrier having holes therein and inserts are placed in the holes. Each insert is made of a softer material than that of the carrier. Wafers are placed into the inserts, and top and bottom surfaces of each wafer are brought into contact with corresponding ones of an upper platen and a lower platen of the processing apparatus for simultaneously removing wafer material from both front and back surfaces of each wafer.
Other objects and features of the present invention will be in part apparent and in part pointed out hereinafter.